This proposal describes how a Statistical Coordinating Unit (SCU) would be organized and operated for an intervention trial to test the efficacy of a diet providing only 20% of calories from fat in reducing breast cancer incidence in women at high risk for this disease. It proposes to locate the SCU at the Fred Hutchinson Cancer Research Center in Seattle, Washington. Participation in a two-month protocol writing effort, a 10-month feasibility study, and a long-term full implementation phase is offered under a cooperative agreement payment mechanism. Proposals for consideration by NCI and units chosen to participate in the trial include a novel trial operation and monitoring plan--and an alternative that is more orthodox. The application concentrates on the role of the SCU in developing eligibility criteria, exclusion criteria, enhancing recruitment and compliance of participants, providing randomization procedures and services, monitoring success in reaching goals in the low-fat diet group, developing unbiased procedures for endpoint determination and monitoring and reporting the efficacy of the intervention if the long-term phase of the trial is undertaken. Database management procedures and quality control methods are described. Statistical considerations are addressed including trial size, analysis methods, and progress reporting. Trial organization and management issues are briefly considered.